Mechanical Bathroom Scale (or weigh scales or scales) are devices to measure weight. Spring balances or spring scales calculate weight that is the product of mass into gravity (9.807 m/s2) on the force on a spring, whereas a balance or pair of scales using a balance beam compares masses by balancing the weight due to the mass of an object against the weight of one or more known masses. Some of them can be calibrated to read in units of force (weight) such as newtons instead of units of mass such as kilograms. The balance or pair of scales using a traditional balance beam to compare masses may read correctly for mass even if moved to a place with a different non-zero gravitational field strength. Also the spring balances that are designed with reading of weight (force) in mind, would read correctly for weight in a different non-zero gravitational field strength.
Scales and balances are widely used in commerce, as many products are sold and packaged by mass.
Although records dating to the 1700s refer to spring scales for measuring mass, the earliest design for such a device dates to 1770 and credits Richard Salter, an early scale-maker. Spring scales came into wide usage in the United Kingdom after 1840 when R. W. Winfield developed the candlestick scale for weighing letters and packages, required after the introduction of the Uniform Penny Post. Postal workers could work more quickly with spring scales than balance scales because they could be read instantaneously and did not have to be carefully balanced with each measurement.
By the 1940s various electronic devices were being attached to these designs to make readings more accurate. Load cells, small nodes that convert pressure (or force) to a digital signal, have their beginnings as early as the late nineteenth century, but it was not until the late twentieth century that they became accurate enough for widespread usage.
A mechanical scale or balance is used to describe a weighing device that is used to measure the mass, force exertion, tension and resistance of an object without the need of a power supply. Types of mechanical scale include spring scales, hanging scales, triple beam balances and force gauges.